LED lighting applications can be made by combining a large number of low power, medium power, or even high power LEDs in a large-area matrix. This matrix will consist of a large number of LEDs in a parallel and series configuration.
It is known to form such a matrix of LEDs in which the LEDs are connected and powered by wires instead of an expensive PCB.
FIG. 1 shows a known arrangement in which an array of LEDs is connected by wires in a grid. A single high voltage rail 10 and a single low voltage rail 12 supply power to the LEDs 14. The LEDs are arranged in a regular matrix in rows and columns. The columns of LEDs have their anodes connected together and their cathodes connected together, with column lines. Thus, each column comprises a set of LEDs in parallel. There is a chain of these columns in series between the voltage rails.
An equivalent circuit diagram is shown in FIG. 2. The LEDs 14 are arranged as a series connection of columns 20. Each column 20 comprises a set of parallel LEDs 14. Note that each LED 14 can itself comprise a package containing several LEDs in series on in parallel.
If there are N columns 20, the voltage between the voltage rails 10, 12 needs to be N times the LED forward bias voltage drop (of for example 3V). The current to be delivered by the power supply is a function of the total number of LEDs.
The design is scalable, and can even be cut to size by shortening the column length. The mesh arrangement shown in FIG. 1 enables all the LEDs to be connected into the circuit with no overlapping wires and with only a single connection to each voltage rail.
The invention addresses the problem that a high voltage is needed if many LEDs are connected in series. For large values of N, the required voltage can become dangerous or can require expensive high-voltage insulation measures. The driving voltage may even exceed the mains voltage.
In order to scale the design, additional rows of LED can be added (so that each column 20 has a greater number of parallel diodes). For each additional row (of N diodes), a dedicated power supply has to be used, in order to deliver the required constant current. The required current depends on the number of LEDs in the mesh.
Thus, although the design in FIG. 1 is scalable, different scaling will require a different power source, which complicates the scaling of the design.